SEEDS Internship : The origin of green-core clinopyroxenes on Fogo

Fogo is a volcanic ocean island in the Cape Verdes in the Atlantic ocean, characterised by particularly alkaline magma compositions. In addition to common normally-zoned clinopyroxene phenocrysts, a population of enigmatic  "green-core" clinopyroxenes has been identified in its lavas. These pyroxenes are unusual in that they contain cores that are much more iron-rich than the rest of the grain, giving them a characteristic green colour in thin section. The cores are often rich in mineral inclusions and are in disequilibrium with the pyroxene rim. The origin of these cores is debated, but they must have crystallised from a different magma to the host, and thus must be xenocrystic. Similar green-core clinopyroxenes are found in alkaline magmas globally, suggesting that the assimilation of evolved clinopyroxene crystals is a common process in these systems and providing broader information about the evolution and structure of the underlying magmatic plumbing.   In this project, a student will characterise the cores of green-core clinopyroxene crystals from Fogo using optical and electron microscopy, including the analysis of in-situ mineral compositions using energy-dispersive X-ray spectroscopy. There will be a particular focus on characterising the mineral inclusion assemblage. The origin of the green-core clinopyroxenes will then be interpreted by relating them to a source lithology that may be present in the deep crust and considering other possible origins of these xenocrysts.

Work plan: Full-time

The student will receive full training in the techniques required. Ideally, the intern should be studying Earth sciences, geology, planetary science or a related subject area, with an interest in igneous petrology. Over the course of the project, the student would develop numerical skills in data processing and modelling. The project is expected to last 6-7 weeks. The student will begin spending around a week reviewing papers and receiving training and relevant background information, then spend the second week on optical microscopy. They will then spend up to eight days over two weeks collecting SEM/EPMA (electron probe microanalysis) images and chemical data. The remainder of the project time will be spent processing, modelling and plotting data, interpretation of findings and preparation of a short report of the findings.

Work plan: Part-time

This internship can be easily adapted to a part-time working pattern. For example, if working 50% FTE, the number of weeks in the above work plan can be multiplied by two. The duration of the internship is only limited by the student's availability and university term dates. There is also a little flexibility in terms of location: laboratory attendance in-person is required, but other parts of the project can be completed remotely if required (though we would encourage attendance if possible, and would provide a workspace).